Production of naphthalene



United States Patent 3,177,262 PRODUCTION OF NAPHTHALEIJE James R. Callrins, Media, Pa, assignor to Sun Oil Company, Philadelphia, Pin, a corporation of New Jersey No Drawing. Filed Apr. 29, 1960, Ser. No. 25,531

' 6 Claims. (Cl. 260-672) This application is a continuation-in-part of mycopending application, Serial No. 671,731, filed July 15, 1957, now abandoned.

This invention relates to the preparation of naphthalene from hydrocarbon stocks. It particularly relates to the method of producing naphthalene from petroleum fractions containing alkylnaphthalenes in admixture with other aromatic and/or non-aromatic hydrocarbons.

Petroleum fractions which boil within the range of 400-550 F. generally contain substantial amounts of alkylnaphthalenes, such as mono-, di-, and .tri-methylnaphthalenes and in smaller quantity, the ethylnaphthw ,lenes. Recycle fractions, which are formed in the cracking of petroleum stocks and which include this boiling range, often contain major proportions of aromatic hydrocarbons that are mainly alkylnaphthalenes. Such fractions typically may have aromatic contents varying within the range of 25-97% but usually contain between 50% and 95% aromatics depending upon the particular operation in which the petroleum fractions are produced. These hydrocarbon charge stocks are obtained in both catalytic and thermal cracking processes and in operations in which combinations of catalytic and thermal cracking steps are utilized. Stock-s having high alkylnaphthalene contents can also be obtained by extracting straight run petroleum fractions of appropriate boiling ranges, such as kerosene, or catalytic fractions such as catalytic gas oil, with solvents, such as furfural or sulfur dioxide, or by selective adsorption with silica gel. These aromatic concentrates may contain 100% aromatic hydrocarbons.

The present invention is directed to the use of hydrothe preparation of naphthalene in high concentration. The charge stock used in practicing the invention is a hydrocarbon fraction boiling substantially Within the range of 400-550" F. but more preferably between 450-- 550 F. and composed by weight of-35l00% aromatic hydrocarbons including substituted condensed ring aro matics such as alkylnaphth-alenes and from 65-0% nonaromatic hydrocarbons. This charge material also commonly contains substantial amounts of sulfur compounds that normally occur Within this boiling range. Charge stocks most typically employed have an aromatic content within the range of 50-95% by weight. In general, the substituted condensed ring aromatics constitute about 20% to 80% of the total aromatic hydrocarbons present in the charge stock.

It has been proposed heretofore to make naphthalene by subjecting stocks of this kind to thermal hydrodealkylation in a single stage at a high temperature in excess of 1300 F. However, this procedure has not proved to be satisfactory for commercial practice for stocks containing substantial amounts of non-aromatic hydrocarbons, for the reason that a highly exothermic reaction occurs that causes the temperature to rise sharply above the level that can'be tolerated safely'in plant operation. In fact, with charge stocks containing only non-aromatic hydrocarbons, it has been found that the exothermic heat of reaction from removing substantially all of the side chains from the moms-tic rings and the addition of hydrogen to form the dealkylated aromatic ring and resultant parafiin product amounts to approximately 500 Btu. per pound of liquid feed. Further, it has been found that when a temperature of about 1125 F. is reached, the hydrocracking of the non-aromatic components begins to take place at such a rate that a rapid temperature rise occurs, with the result that the overall hydrocracking reaction takes place progressively faster and the temperature becomes uncontrollable. In short, the reaction is designated as runaway.

In addition, the dealkylation reaction, apart from the hydrocracking reaction, necessary to produce naphthalene from the above-described charge stocks is extremely exothermic. In some cases, the temperature rise due to the dealkylation reaction has been as much as 100 F. Therefore, the operating conditions of such a process, even with 100% aromatic content charge stocks, become difficult to control.

The present invention provides a method of making naphthalene from change stocks as specified above wherein the temperature rise due to the hydrocracking of the non-aromatics and the dealkylation of the aromatics is minimized and controlled.

According to the invention, the charge material is first subjected to a conditioning treatment in the presence of a desulfurization catalyst and added hydrogen under conditions including a temperature within the range of 800- 980 F., at which the non-aromatic components are converted to lower boiling compounds at a slow enough rate to prevent excessive temperature rise. Under these conditions, substantial conversion of the alkylnaphthalenes into naphthalene does not occur. In addition, a minor proportion of the aromatic hydrocarbons are at least partially hydrogenated. The conditioned reaction product from this first step is then subjected in a second step to a temperature above 1000 .F., whereby deallrylation of the alkylnaphthalenes and dehydrogenation of the minor proportion of the aromatic hydrocarbons occurs. Due to the fact that the non-aromatic components have already been largely removed in the first reaction stage, the temperature in this second stage reaction does not rise excessively. Furthermore, those aromatic hydrocarbons which were hydrogenated in the first step are dehydrogenated in the second step thereby additionally aiding in the temperature control of the second step due to the endothermic nature of the dehydrogenation reaction. The final reaction product is fractionated to obtain naphthalene in high concentration.

Thus, the present invention is a two-stage process for making naphthalene from a hydrocarbon charge stock wherewith by removing the non-aromatics in the first stage and'by regulating the temperature in the first stage to vary the degree of aromatic saturation, it is possible to control the temperature rise during the second stage. Further, better temperature control is realized in the first stage with charge stocks containing non-aromatics since the exothermic addition of hydrogen to the aromatic hydrocarbons and to the cleaved carbon-carbon bonds tends to counterbalance the endothermic cracking of the nonaromatic hydrocarbons. On the other hand, when charging aromatic charge stocks, the exothermic addition of hydrogen to the aromatic hydrocarbons provides additional heat so that the desired first stage temperature can be obtain-ed Without excessive external heat requirements. In the second stage, the endothermic dehydrogenation of the hydrogenated aromatics from the first stage reaction at least partially counterbalances the exothermic dealkylation reaction of the alkylnaphthalenes thereby providing better temperature control.

The term hydrocracking" primarily defined as the cumulative result of cleaving, i.e. cracking, carbon carbon bonds and of adding hydrogen to the cleaved bonds. The overall hydrocracking reaction is generally exother- 1111C.

than that due to sulfur removal alone.

,7 cci The term dealkylation is primarily defined: as the cumulative result of removing the alkyl side chains from the substituted condensed ring aromatic hydrocarbons and of adding hydrogen to form the 'dealkylated condensed The overall dealkylation reactionis generally exothermic.

ring aromatic hydrocarbons.

in this invention, the term hydrocracking will also include the hydrogenation of a minor proportion of the aromatic hydrocarbonsand the term dealkylation will include the dehydrogenating of those aromatics hydrogenated during hydrocracking.

The critical feature of the first stage reaction is to condition the first stage product by balancing hydrogenation, cracking, and desulfurization in such a manner that example, if the dicyclic aromatic is considered to be naphthalene, then the equilibrium relationship for-the reaction:

naphthalene-i-Z hydrogenetetrahydronapthalene at 300 p.s.i.g. was found to be as follows.

Temp, F.: K=equilibrium constant 980 15.8 800 4,000

Thus, it is seen that at 300 p.s.i.g., by regulating the temperature of the reaction, the degree of hydrogenation of It is noted that substantial naphthalene can be varied.

saturation occurs at 800 F. asv evidenced by the high value of the equilibrium constant, K. On the other hand,

Example 1 Operating conditions:

P=500 p.s.i.g. Space ve1ocity=1 Hydrogen recycle-11,000 s.c.f./ barrel Catalyst: CoMo on alumina Results: 7

Hydrogen consumption=300 s.f.c. barrel Sulfur content of product: 0.01%

Since hydrogen consumption for sulfur removal alone would be expected to be about 6575 sci/barrel (standcompounds in the charge stock toliydrogen sulfide. The

naphthalene recovered from the, final reaction product carbon mole ratio of 3:1 to '25 :1 and preferably 5:1 to

15: 1, and a liquid hourly space velocity of 0.2 to (volumes of chargeper hour per bulk volume of catalyst). The hydrogen consumption under these conditions should be between 65-500 s.c.f. per barrel of liquid feed per percent sulfur in the feed and preferably between 200 and 400 -s.c.f./barrel. The. conditions for the second stage thermal treatment include a pressure of 150-1000 p.s.i.g., prefenably 200-500 p-.=s.i.g., a hydrogen to hydrocarbon mole ratio within the range of 3:1 to 25: 1 and preferably 5:1 to :1, a residence time of 2300 seconds with a preferred-residence time of; 10-60 seconds, and a tern perature above 1000 F., preferably withinthe range of 12001400 F., sutficient to elfect a dealkylation of the alkylnaphthalenes while dehydrogenating the minor proportion of. hydrogenated aromatic hydrocarbons.

A still further manner practicing the invention involves catalyticallyconditioning the charge under the conditions set forth for the embodiment first mentioned above and then catalytically dealkylating the alkylnaphthalenes in the presence of a desulfurizationcatalyst. The presence of the catalyst in the latter. step facilitates the dealkylation reaction and in some-cases permits'it to be carried out at a lower temperature than that required for thermal dealkylation. The oatalystalso effects the conversion of any remaining sulfur into hydrogen sulfide and hence permits the preparation of naphthalene having negligible sulfur content. The conditions for the catalytic dealkylation step'include a pressure of 150-1000 p.s.i.g. with a range of 200-500 p.s.i.'.g. preferred, a hydrogen to hydrocarbon mole ratio .of 5 :1 to 1,.a liquid hourly space velocity of; 0.2-5.0, and a temperature above l000 F., usually betweenllOOF. and 1200 F., sulficient'to dealkylate' the alkylnaphthalenes, convert any remaining sulfur mainly into hydrogen sulfide and de- 'hydrogenate the minor proportion of hydrogenated aroard cubic feet per barrel of feed) for each 1% S in the feed, it is seen: that the hydrogen consumption of 300 set/barrel per 0.6% S in feedis about 5-10 times larger.

The remainder of the hydrogen is used in partial ring saturation as would be predicted from the equilibrium relationship discussed hereinabove.

In a preferred embodiment of the invention, the first conditioning step is carried out in the-presence of a catalyst and added hydrogen while the second step involves a thermal treatment to effect dealkylation of the alky- V of the aromatic hydrocarbons is to be obtained. At the.

same time, it effects desulfurization by converting sulfur matic hydrocarbons.

In practicing any-of the foregoing embodiments of the I invention, the total reaction product from the first conditioning step can be charged to the second step. However, it is-preferable to subject the first reaction product.

to distillation to obtain a fraction boiling mainly in the range of 400-550 -F. for use as charge to the second step. This distillation removes material formed in the first hydrocracking reaction which boilsbelow .400 F. and which will not contributeto the formation of naph thalene inthe second reaction stage... It also removes a minor amount of polymeric material that boils above 550 P. which would tend to contribute to coke formation if allowed to remain in the charge to thesecondstep.

In both the first and second reaction stages of each of theforegoing embodiments, coking occurs after a time to such extent that coke removal from the reaction zone is required. This can 'be done in conventional manner by passing an oxygen-containing gas through the reaction zone to burn out the coke. In the steps inwhich a desulfurizing catalyst is used,.burning of coke from the catalyst restores its catalytic activity.

The following are examples of certain embodimentsof the invention: p

' Example 11 A chargestock was prepared by distilling a gas oil fraction obtained by a combination or, catalytic and thermal cracking operations. The charge stock had a boiling range of 460-500 :F., an aromatic hydrocarbon content of 78% by weight, including about 1% naphthalene, and a sulfur content of.0.25 Hydrogen was mixed with the charge in a mole ratio of :1 and the mixture was heated to 900 F. and fed in vapor phase into a catalytic hydrocracking zone at a pressure of 500 p.s.i.g. Thecatalyst was a cobalt molybdate on alumina'desulfurizing catalyst containing 3% cobalt and molybdenum. The liquid space velocity of the charge in the reaction zone was 1 vol./vol. of catalyst/hr. The reaction product contained 8.3% of C -400 F. fraction having an F-l clear octane rating of 82.7 and 86.1% of material boiling above 400 F.

C and lighter hydrocarbons 37.0 C 400 F. fraction 15.0 400450 F. fraction 23.0 450 F. and heavier 24.6

The 400-450 F. fraction was composed predominantly of naphthalene and had a freezing point of 786 C. and a sulfur content of 0.06%. The higher boiling fraction contained a small amount of naphthalene due to imperfect fractionation. Overall yield of naphthalene, based on the original charge stock was 23.7%.

Example III The charge stock prepared as in Example II was subjected to a conventional thermal hydrodealkylation treatment, omitting the first conditioning step of the invention. The charge stock'was admixed with hydrogen in a mole ratio of hydrogen to hydrocarbon of 10:1 under a pressure of 200 p.s.i.g. Heat was applied at a sufiicient rate to raise the temperature of the mixture to 1300 F. But beginning at a temperature of about 1125 F., the temperature rose rapidly to above 1600 F. before the reaction could be stopped. This was a characteristic runaway reaction.

Example IV A catalytic gas oil was solvent extracted with furfural to prepare aromatic concentrates of varying aromatic contents. These aromatic concentrates were first subj'ected to catalytic conditioning and then thermal dealkylation. The results, indicating temperature control characteristics, are as follows:

Sample A B C D Aromatic Content 96. 2 Q0. 5 84.0 75. 0 First Stage:

Temp, F 925 875 900 900 Press. p.s.i.g 500 500 500 500 LHSV, v.v./hr 0.86 1 1 1 Recycle gas rate, s.c.l./b 3,000 7, 750 5, 060 10, S50 Catalyst Co-Mo Co-Mo Co-Mo Co-Mo Second Stage:

Inlet Temp., F 1, 200 1, 200 1, 200 1,200 Max. Temp, F 1, 330 1, 320 1, 315 1, 295 Press., p.s.i.g 200 200 200 200 Residence Time, Sec 12.7 12. 5 13. 2 13. 3 Naphthalene yield, wt.

percent of charge 31. 8 23. 3 21. 8 22. 8

The above data indicate the temperature control technique of the invention by varying the first step conditioning temperature. In comparison to Sample A, Sample B had a lower aromatic content and was processed at a lower temperature thereby hydrogenating the aromatics to a greater extent according to the equilibrium relationship. In addition, the lower temperature cracked less of the non-aromatics. Accordingly, the greater hydrogenation of Sample B with subsequent dehydrogenation in the second step elfectively counterbalanced the exothermic reactions of the second step. Sample A had less nonaromatics to crack and the higher temperature of the first step "hydrogenated the aromatics to a lesser extent'but cracked the non-aromatics to a greater extent. However,

the temperature rise in the second stage was greater. Similarly, Samples C and D had 84% and 75% aromatic parting from the spirit of the invention. For example, the

undealkylated alkylnaphthalenes can be recycled to the process to effect greater yields.

I claim:

1. A two-stage process for making naphthalene from a sulfur-containing petroleum fraction boiling mainly within the range of 400* F. to 550 F. and composed of at least 50% aromatic hydrocarbons comprising mainly alkylnaphthalenes and the remainder comprising mainly non-aromatic hydrocarbons which comprises subjecting said petroleum fraction to conditioning treatment in the presence of a desulfurization catalyst and added hydrogen under reaction conditions including a temperature between 800 and 980 F. and a pressure between and 1000 p.s.i.g.; regulating the temperature, pressure, and amount of hydrogen added in said conditioning step to eflfect hydrogen consumption of from 65 to 500 standard cubic feet per percent sulfur in said petroleum fraction per barrel of said petroleum fraction to convert nonaromatic hydrocarbons to lower boiling compounds, to convert sulfur mainly to hydrogen sulfide, and to at least partially hydrogenate a minor proportion of the aromatic hydrocarbons without substantial conversion of the alkylnaphthalenes to naphthalene; subjecting conditioned reaction product boiling mainly within the range of 400 F. to 550 F. to thermal treatment in the presence of added hydrogen at a pressure between 150 and 1000 p.s.i.g., a hydrogen to hydrocarbon mole ratio of from 3 :1 to 25: 1, a residence time of from 2 to 300 seconds, and a temperature above 1000 F. sufficient to effect dealkylation of alkylnaphthalenes and dehydrogenation of said hydrogenated aromatic hydrocarbons; and fractionating the final reaction product to recover naphthalene in high concentration.

2. A two-stage process according to claim 1 wherein said petroleum fraction is selected from the group consisting of aromatic concentrates separated from cracked gas-oil and aromatic concentrates separated fnom straight run petroleum fractions.

3. A two-stage process according to claim 2 wherein said petroleum fraction is an aromatic concentrate separated from cracked gas oil.

4. A two-stage process for making naphthalene from a sulfur-containing petroleum fraction boiling mainly within the range of 400 F. to 550 F. and composed of at least 50% aromatic hydrocarbons comprising mainly alkylnaphthalenes and the remainder comprising mainly the presence of a desulfurizatio-n catalyst and added hydrogen under reaction conditions including a temperature between 800 and 980 F. and a pressure between 150 and 1000 p.s.i.g.; regulating the temperature, pressure, and amount of hydrogen added in said conditioning step to effect hydrogen consumption of from 65 to 500 standard cubic feet per percent sulfur in said petroleum frac tion per barrel of said petroleum fraction to convert nonaromatic hydrocarbons to lower boiling compounds, to convert sulfur mainly to hydrogen sulfide, and to at least partially hydrogenate a minor proportion of the aromatic hydrocarbons without substantial conversion of the alkylnaphthalenes to naphthalene; subjecting conditioned reaction product boiling mainly within the range of 400 F. to 550 F. to catalytic dealkylation in the presence of eX- cess added hydrogen and a desulfurization catalyst at a pressure of between 150 and 1000 p.s.i.g., a hydrogen to hydrocarbon mole ratio of from 5:1 to 25:1, a liquid hourly space velocity of from 0.2 to 5:0, and a temperature above 1000" F. sufi'lcient to dealkylate said alkylnaphthalenes, to convert any remaining sulfur mainly into hydrogen sulfide, and to dehydrogenate said hydrogenated aromatic hydrocarbons; and fractionating the final reaction product to recover in high concentration naphthalene having low sulfur content.

5. A two-stage process according to claim 4 Where-in said petroleum fraction is selected from the group consisting of aromatic. concentrates separated from cracked gas oil and aromatic concentrates separated from straight run petroleum fractions.

6. A two-stage process according to claim 5 wherein saidpetroleum fraction is an aromatic concentrate. separated'frorn cracked gas. oil. 7

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Nelson: Petroleum Refinery Engineering, 4th edition, 1958, McGraw-Hill, N.Y;, pp. 177-179.

:ALPHONSO D. SULLIVAN, Primary Examiner.

M ILTON STERMAN, IAMES S. BAILEY,vExamine rs. 

1. A TWO-STAGE PROCESS FOR MAKING NAPHTHALENE FROM A SULFUR-CONTAINING PETROLEUM FRACTION BOILING MAINLY WITHIN THE RANGE OF 400*F. TO 550*F. AND COMPOSED OF AT LEAST 50% AROMATIC HYDROCARBONS COMPRISING MAINLY ALKYLNAPHTHALENES AND THE REMAINDER COMPRISIANG MAINLY NON-AROMATIC HYDROCARBONS WHICH COMPRISES SUBJECTING SAID PETROLEUM FRACTION TO CONDITIONING TREATMENT IN THE PRESENCE OF DESULFURIZATION CATALYST AND ADDED HYDROGEN UNDER REACTIN CONDITIONS INCLUDING A TEMPERATURE BETWEEN 800* AND 980*F. AND A PRESSURE BETWEEN 150 AND 1000 P.S.I.G.; REGULATING THE TEMPERATURE, PRESSURE, AND AMOUNT OF HYDROGEN ADDED IN SAID CONDITINING STEP TO EFFECT HYDROGEN CONSUMPTION OF FROM 65 TO 500 STANDARD CUBIC FEET PER PERCENT SULFUR IN SAID PETROLEUM FRACTION PER BARREL OF SAID PETROLEUM FRACTION TO CONVERT NONAROMATIC HYDROCARBONS TO LOWER BOILING COMPOUNDS, TO CONVERT SULFUR MAINLY TO HYDROGEN SULFIDE, AND TO AT LEAST PARTIALLY HYDROGENATE A MINOR PROPORTION OF THE AROMATIC HYDROCARBONS WITHOUT SUBSTANTIAL CONVERSION OF THE ALKYLNAPHTHALENES TO NAPHTHALENE; SUBJECTING CONDITIONED REACTION PRODUCT BOILING MAINLY WITHIN THE RANGE OF 400*F. TO 550*F. TO THERMAL TREATMENT IN THE PRESENCE OF ADDED HYDROGEN AT A PRESSURE BETWEEN 150 AND 1000 P.S.I.G., A HYDROGEN TO HYDROCARBON MOLE RATIO OF FROM 3:1 TO 25:1, A RESIDENCE TIME OF FROM 2 TO 300 SECONDS, AND A TEMPERATURE ABOVE 1000*F. SUFFICIENT TO EFFECT DEALKYLATION OF ALKYLNAPHTHALENES AND DEHYDROGENATION OF SAID HYDROGENATED AROMATIC HYDROCARBONS; AND FRACTIONATING THE FINAL REACTION PRODUCT TO RECOVER NAPHTHALENE IN HIGH CONCENTRATION. 